The invention relates to a process for the manufacture of superconducting cavity resonators and more particularly to the manufacture of superconducting cavity resonators having cavities lined with niobium nitride NbN. 2. Description of the Prior Art
Superconducting cavity resonators are becoming increasingly important because their use makes possible high degrees of efficiency in accelerators for ionized particles.
Most superconducting high-frequency resonators are based on niobium (Nb). Since the losses are very low in such resonators, new surface effects are observed quantitively and qualitatively, which are responsible for the performance of superconducting resonators, which differ significantly from the results which might be expected from resonators with ideal surfaces.
The quality of superconducting resonators depends to a very great extent on the surface characteristics and quality of the cavities.
Niobium resonators themselves, on account of the critical temperature T.sub.c.congruent. 9 K at 4.2 K, do not have high field strengths and high-frequency qualities. These properties of niobium resonators are discussed in a thesis by J. Halbritter, University at Karlsruhe and Kernforschungszentrum Karlsruhe (KfK), Karlsruhe, Federal Republic of Germany, 1984, at pages 102, 104 and 124. Also, the thesis indicated that radiation damage occurred in heavily oxidized niobium cavities.
Nb.sub.3 Sn resonators, of course on account of a T.sub.c.congruent. 18 K, have the potential of achieving high critical fields and high frequency qualities even at 4.2 K, but they exhibit a poor surface quality. These mediocre results with Nb.sub.3 Sn have been obtained for various preparation techniques and surface treatments in all labs working with Nb.sub.3 Sn. (See IEEE Transactions on Magnetics, Vol. Mag-15, No. 1, January 1979, Kneisel, Stoltz, Halbritter, entitled, "Measurements of Supeconducting Nb.sub.3 Sn Cavities in the GHz Range".
NbN coatings on niobium surfaces are described in Journal of Applied Physics 52 (1981) 921, Isagawa. The NbN is deposited on the surface by sputtering, but that process produces poor quality and low field strengths, although a critical temperature of T.sub.c.congruent. 16 K is achieved.
Some examples of superconducting cavity resonators are found in U.S. Pat. No. 4,414,487, entitled "Superconducting Electron Beam Generator" and U.S. Pat. No. 4,227,153, entitled "Pulse Generator Utilizing Superconducting Apparatus". Some examples of cryogenics and related matter are found in the following references: Advances in Cryogenic Engineering, P. Kneisel, O. Stoltz, J. Halbritter, Vol. 22 Plenum Press, New York, 1977), p.341; IEEE Transactions MAG-13, P. Kneisel, H. Kupfer, W. Schwarz, O. Stoltz, J. Halbritter, 496 (1977); Advances in Cryogenic Engineering, P. Kneisel, H. Kupfer, O. Stoltz, J. Halbritter, Vol. 24 (Plenum Press, New York, 1978), p.442; Proc. 15th Int. Conf. on Low Temperature Physics, J. Halbritter, Grenoble, 1978; J. de Physique C6, 396 (1978); IEEE Transactions MAG-11, 427 (1975); Int. Bericht, P. Kneisel, W. Meyer, (IK Kernforschungszentrum, Karlsruhe, 1978); Z. Phys. 266, J. Halbritter, 209 (1974); J. Appl. Phys. 48, W. Schwarz, J. Halbritter, 4618 (1977); and Appl. Superconduct. Conf., Annapolis, 1972, J. Halbritter, 1972 (IEEE, N.Y. 1972), p. 662. All of the above-mentioned documents and patents are incorporated herein by reference as if the contents thereof were set forth herein in their entirety.